dt-bindings: watchdog: sama5d4-wdt: add compatible for sama7g5-wdt

This driver is also compatible with the watchdog on sama7g5 SoC.
Add the corresponding compatible string to the binding.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20210527100120.266796-3-eugen.hristev@microchip.com
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>